Unfortunately if you start with a 64, then there isn't any internal memory expansion board. If you're building a brand new board, then using a single 512k SRAM is much easier than using multiple 41256 chips.

If you are good at electronics and soldering, there's a relatively easy modification to the internal expansion module to upgrade it to 256 kB. There you can find the description. Unfortunately, in Hungarian only.

The most important parts are the linked schematics (1. ábra and 2. ábra; pointing to the top and bottom parts of the very same picture). The top part of the schematic shows the modification on the address multiplexing. The bottom part shows the modification on the DRAM refresh logic.

The instructions go something like this:
Replace the 4164 DRAM ICs with 41256s.
A16, A17 and A18 must be connected to the (top) 74LS151 multiplexer. Its output must be connected to pin 2 of U110.
Disconnect A16 from pin 2 of U112 and connect pin 2 to ground.
Disconnect A17 from pin 1 of U110 and connect pin 1 to +5 Volts.
Disconnect A18 from pin 2 of U110 and connect pin 2 to pin 5 of 74LS151.
Switch SW will disable the expansion if closed and enable it if opened in the contiguous ECh-F7h segment range.
Disconnect pin 12 of U109 from pin 9 of all DRAM ICs.
Connect pin 1 of all (new) DRAM ICs and connect them to pin 12 of U109.
Connect pin 9 of all DRAM ICs to pin 5 of (bottom) 74LS151 multiplexer.
MUX signal can be taken from pin 1 of U108 or U109.
The three TTL ICs can be piggy-backed on components already there on the board but the DRAMs are recommended to be seated in sockets.

Unfortunately, I know next to nothing about electronics, therefore I can't guarantee that my translation makes any sense at all.

We're trying to do something. Unfortunately, there have been so many problems lately (this is understandable).

The SF3 is interesting, but it seems to offer far more than I'd personally want.

As someone that recently bought one of the new/almost-new Enterprise 64 machines that have been unearthed in Egypt, I just want some more internal memory, and Szorg's lovely SD card adapter.

From what I have seen posted online, the folks here once got a 512KB expansion board simplified down to using just a 512KBx8 SRAM chip, and a 74LS138 decoder chip, plus some decoupling capacitors.

Does anyone remember seeing a circuit diagram for that anywhere?

If so, then I might be able to persuade a friend to actually produce a board layout that could be ordered from one of the cheap prototyping companies.

These days, it seems pretty easy (and cheap) to get a small batch of unpopulated circuit boards made, so perhaps that would be one solution for those of us that would like to get an internal memory expansion?

I don't see the names of the ROMs.
(startup bank: 0, Actual bank: 0)

These are test names that I have put in my EP.... put them you also on your EP if you like them... or better put your own names.

Remember to remove Rom definitions on the INI file if you use Rombanks at the same segments.

To define Roms, first you have to store the original Roms on a directory defined by you, for example on the root of the USB(drive 1). Then search the Roms on the ROM Manager program.

I don't see the names of the ROMs.
(startup bank: 0, Actual bank: 0)